Handover Resource Allocation

8.4.2.1 General

The purpose of the Handover Resource Allocation procedure is to reserve resources at the target eNB for the handover of a UE.

8.4.2.2 Successful Operation

HANDOVER REQUEST

MME

HANDOVER REQUEST ACKNOWLEDGE target

eNB

Figure 8.4.2.2-1: Handover resource allocation: successful operation

The MME initiates the procedure by sending the HANDOVER REQUEST message to the target eNB. The

HANDOVER REQUEST message may contain the Handover Restriction List IE, which contains roaming or access restrictions.

If the Handover Restriction List IE is contained in the HANDOVER REQUEST message, the target eNB shall store this information in the UE context. This information shall however not be considered whenever one of the handed over E-RABs has a particular ARP value (TS 23.401 [11]).

The target eNB shall use the information in Handover Restriction List IE if present in the HANDOVER REQUEST message to

- determine a target for subsequent mobility action for which the eNB provides information about the target of the mobility action towards the UE;

- select a proper SCG during dual connectivity operation.

If the Handover Restriction List IE is not contained in the HANDOVER REQUEST message, the target eNB shall consider that no roaming and no access restriction apply to the UE.

Upon reception of the HANDOVER REQUEST message the eNB shall store the received UE Security Capabilities IE in the UE context and use it to prepare the configuration of the AS security relation with the UE.

If the SRVCC Operation Possible IE is included in the HANDOVER REQUEST message, the target eNB shall store the content of the received SRVCC Operation Possible IE in the UE context and, if supported, use it as defined in TS 23.216 [9].

Upon reception of the HANDOVER REQUEST message the eNB shall store the received Security Context IE in the UE context and the eNB shall use it to derive the security configuration as specified in TS 33.401 [15].

If the Trace Activation IE is included in the HANDOVER REQUEST message, the target eNB shall if supported, initiate the requested trace function as described in TS 32.422 [10]. In particular, the eNB shall, if supported:

- if the Trace Activation IE does not include the MDT Configuration IE, initiate the requested trace session as described in TS 32.422 [10];

- if the Trace Activation IE includes the MDT Activation IE, within the MDT Configuration IE, set to “Immediate MDT and Trace”, initiate the requested trace session and MDT session as described in TS 32.422 [10];

- if the Trace Activation IE includes the MDT Activation IE, within the MDT Configuration IE, set to “Immediate MDT Only”, “Logged MDT only” or “Logged MBSFN MDT”, initiate the requested MDT session as described in TS 32.422 [10] and the target eNB shall ignore Interfaces To Trace IE, and Trace Depth IE.

- if the Trace Activation IE includes the MDT Location Information IE, within the MDT Configuration IE, store this information and take it into account in the requested MDT session.

- if the Trace Activation IE includes the Signalling based MDT PLMN List IE, within the MDT Configuration IE, the eNB may use it to propagate the MDT Configuration as described in TS 37.320 [31].

- if the Trace Activation IE includes the MBSFN-ResultToLog IE, within the MDT Configuration IE, take it into account for MDT Configuration as described in TS 37.320 [31].

- if the Trace Activation IE includes the MBSFN-AreaId IE in the MBSFN-ResultToLog IE, within the MDT Configuration IE, take it into account for MDT Configuration as described in TS 37.320 [31].

- if the Trace Activation IE includes the UE Application layer measurement configuration IE, initiate the requested trace session and QoE Measurement Collection function as described in TS 36.300 [14].

- if the Trace Activation IE includes the Bluetooth Measurement Configuration IE, within the MDT Configuration IE, take it into account for MDT Configuration as described in TS 37.320 [31].

- if the Trace Activation IE includes the WLAN Measurement Configuration IE, within the MDT Configuration IE, take it into account for MDT Configuration as described in TS 37.320 [31].

- if the Trace Activation IE includes the MDT Configuration NR IE, store and forward the MDT Configuration NR IE to the SgNB, if the eNB has configured EN-DC for the UE.

If the CSG Id IE is received in the HANDOVER REQUEST message, the eNB shall compare the received value with the CSG Id broadcast by the target cell.

If the CSG Membership Status IE is received in the HANDOVER REQUEST message and the CSG Membership Status is set to “member”, the eNB may provide the QoS to the UE as for member provided that the CSG Id received in the HANDOVER REQUEST messages corresponds to the CSG Id broadcast by the target cell.

If the CSG Membership Status IE and the CSG Id IE are received in the HANDOVER REQUEST message and the CSG Id does not correspond to the CSG Id broadcast by the target cell, the eNB may provide the QoS to the UE as for a non member and shall send back in the HANDOVER REQUEST ACKNOWLEDGE message the actual CSG Id broadcast by the target cell.

If the target cell is CSG cell or hybrid cell, the target eNB shall include the CSG ID IE in the HANDOVER REQUEST ACKNOWLEDGE message.

If the target eNB receives the CSG Id IE and the CSG Membership Status IE is set to “non member” in the

HANDOVER REQUEST message and the target cell is a closed cell and at least one of the E-RABs has a particular ARP value (see TS 23.401 [11]), the eNB shall send back the HANDOVER REQUEST ACKNOWLEDGE message to the MME accepting those E-RABs and failing the other E-RABs.

If the Subscriber Profile ID for RAT/Frequency priority IE is contained in the Source eNB to Target eNB Transparent Container IE, the target eNB shall store the content of the received Subscriber Profile ID for RAT/Frequency priority IE in the UE context and use it as defined in TS 36.300 [14].

If the Additional RRM Policy Index IE is contained in the Source eNB to Target eNB Transparent Container IE, the target eNB shall, if supported, store it and use it as defined in TS 36.300 [14].

Upon reception of the UE History Information IE, which is included within the Source eNB to Target eNB Transparent Container IE in the HANDOVER REQUEST message, the target eNB shall collect the information defined as

mandatory in the UE History Information IE and shall, if supported, collect the information defined as optional in the UE History Information IE, for as long as the UE stays in one of its cells, and store the collected information to be used for future handover preparations.

Upon reception of the UE History Information from the UE IE, which is included within the Source eNB to Target eNB Transparent Container IE in the HANDOVER REQUEST message, the target eNB shall, if supported, store the collected information, to be used for future handover preparations.

If the Mobility Information IE is included within the Source eNB to Target eNB Transparent Container IE in the HANDOVER REQUEST message, the target eNB shall, if supported, store this information and use it as defined in TS 36.300 [14].

If the Emergency Indicator IE is included within the Source eNB to Target eNB Transparent Container IE in the HANDOVER REQUEST message, the target eNB shall, if supported, use it to allocate radio bearer resources as specified in TS 23.502 [51].

If the Expected UE Behaviour IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, store this information and may use it to determine the RRC connection time.

If the Bearer Type IE is included in the HANDOVER REQUEST message and is set to "non IP", then the eNB shall not perform IP header compression for the concerned E-RAB.

If the Ethernet Type IE is included in the HANDOVER REQUEST message and is set to "True", then the eNB shall, if supported, take this into account to perform header compression appropriately for the concerned E-RAB.

In case of inter-system handover from gNB with direct forwarding, if the target eNB receives the UE Context Reference at Source IE in the Source eNB to Target eNB Transparent Container IE, it may use it for internal forwarding as specified in TS 37.340 [47].

After all necessary resources for the admitted E-RABs have been allocated, the target eNB shall generate the HANDOVER REQUEST ACKNOWLEDGE message. The target eNB shall include in the E-RABs Admitted List IE the E-RABs for which resources have been prepared at the target cell. The E-RABs that have not been admitted in the target cell, if any, shall be included in the E-RABs Failed to Setup List IE.

If the HANDOVER REQUEST message contains the Data Forwarding Not Possible IE associated with a given E-RAB within the E-RABs To Be Setup List IE set to “Data forwarding not possible”, then the target eNB may decide not to include the DL Transport Layer Address IE and the DL GTP-TEID IE and for intra LTE handover the UL Transport Layer Address IE and the UL GTP-TEID IE within the E-RABs Admitted List IE of the HANDOVER REQUEST ACKNOWLEDGE message for that E-RAB.

For each bearer that target eNB has decided to admit and for which DL forwarding IE is set to “DL forwarding proposed”, the target eNB may include the DL GTP-TEID IE and the DL Transport Layer Address IE within the E-RABs Admitted List IE of the HANDOVER REQUEST ACKNOWLEDGE message indicating that it accepts the proposed forwarding of downlink data for this bearer.

If the HANDOVER REQUEST ACKNOWLEDGE message contains the UL GTP-TEID IE and the UL Transport Layer Address IE for a given bearer in the E-RABs Admitted List IE, then it means the target eNB has requested the forwarding of uplink data for this given bearer.

If the Request Type IE is included in the HANDOVER REQUEST message, then the target eNB should perform the requested location reporting functionality for the UE as described in subclause 8.11.

If the UE Security Capabilities IE included in the HANDOVER REQUEST message only contains the EIA0 algorithm as defined in TS 33.401 [15] and if this EIA0 algorithm is defined in the configured list of allowed integrity protection algorithms in the eNB (TS 33.401 [15]), the eNB shall take it into use and ignore the keys received in the Security Context IE.

The GUMMEI IE shall only be contained in the HANDOVER REQUEST message according to subclauses 4.6.2 and 4.7.6.6 of TS 36.300 [14]. If the GUMMEI IE is present, the target eNB shall store this information in the UE context and use it for subsequent X2 handovers.

The MME UE S1AP ID 2 IE shall only be contained in the HANDOVER REQUEST message according to subclause 4.6.2 of TS 36.300 [14].If the MME UE S1AP ID 2 IE is present, the target eNB shall store this information in the UE context and use it for subsequent X2 handovers.

If the Management Based MDT Allowed IE only or the Management Based MDT Allowed IE and the Management Based MDT PLMN List IE is contained in the HANDOVER REQUEST message, the target eNB shall, if supported, store the received information in the UE context, and use this information to allow subsequent selections of the UE for management based MDT defined in TS 32.422 [10].

If the Masked IMEISV IE is contained in the HANDOVER REQUEST message the target eNB shall, if supported, use it to determine the characteristics of the UE for subsequent handling.

If the HANDOVER REQUEST contains a Target Cell ID IE, as part of the Source eNB to Target eNB Transparent Container IE, for a cell which is no longer active, the eNB may respond with an HANDOVER REQUEST

ACKNOWLEDGE in case the PCI of the deactivated cell is in use by another active cell.

If the ProSe Authorized IE is contained in the HANDOVER REQUEST message and it contains one or more IEs set to

“authorized”, the eNB shall, if supported, consider that the UE is authorized for the relevant ProSe service(s).

If the UE User Plane CIoT Support Indicator IE is included in the HANDOVER REQUEST message and is set to

"supported", the eNB shall, if supported, consider that User Plane CIoT EPS Optimisation as specified in TS 23.401 [11] is supported for the UE.

If the CE-mode-B Support Indicator IE is included in the HANDOVER REQUEST ACKNOWLEDGE message and set to "supported", the MME shall, if supported, take this information into account when setting NAS timer values for the UE as specified in TS 24.301[24].

If the V2X Services Authorized IE is contained in the HANDOVER REQUEST message and it contains one or more IEs set to “authorized”, the eNB shall, if supported, consider that the UE is authorized for the relevant service(s).

If the UE Sidelink Aggregate Maximum Bit Rate IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, use the received value for the concerned UE’s sidelink communication in network scheduled mode for V2X services.

If the Enhanced Coverage Restricted IE is included in the HANDOVER REQUEST message, the eNB shall store this information in the UE context and use it as defined in TS 23.401 [11].

If the CE-Mode-B Restricted IE is included in the HANDOVER REQUEST message and the Enhanced Coverage Restricted IE is not set to restricted and the Enhanced Coverage Restricted information stored in the UE context is not set to restricted, the eNB shall store this information in the UE context and use it as defined in TS 23.401 [11].

If the NR UE Security Capabilities IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, store this information in the UE context and use it as defined in TS 33.401 [15].

If the Aerial UE subscription information IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, store this information in the UE context and use it as defined in TS 36.300 [14].

If the Pending Data Indication IE is included in the HANDOVER REQUEST message, the eNB shall use it as defined in TS 23.401 [11].

If the Subscription Based UE Differentiation Information IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, store this information in the UE context for further use according to TS 23.401 [11].

If the Additional RRM Policy Index IE is contained in the HANDOVER REQUEST message, the eNB shall, if supported, store it and use it as defined in TS 36.300 [14].

If the HANDOVER REQUEST message is received for an handover originating from a source NG-RAN node, the list of E-RABs contained in the source eNB to target eNB Transparent Container which are not included in the

HANDOVER REQUEST message shall be considered as not to be handed over and ignored.

If the IAB Authorized IE is contained in the HANDOVER REQUEST message, the target eNB shall, if supported, consider that the handover is for an IAB-node.

If the NR V2X Services Authorized IE is contained in the HANDOVER REQUEST message and it contains one or more IEs set to “authorized”, the eNB shall, if supported, consider that the UE is authorized for the relevant service(s).

If the NR UE Sidelink Aggregate Maximum Bit Rate IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, use the received value for the concerned UE’s sidelink communication in network scheduled mode for NR V2X services.

If the PC5 QoS Parameters IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, use it for the concerned UE’s NR sidelink communication as specified in TS 23.285 [49].

If the Inter-system measurement Configuration IE is included within the Source eNB to Target eNB Transparent Container IE in the HANDOVER REQUEST message, the target eNB shall, if supported, use it as defined in TS 38.300 [45]. The Inter System Measurement Configuration IE shall contain at least one of the RSRP, RSRQ or SINR

thresholds. If only one of the thresholds is present, the LTE eNB shall use the present threshold to compare against the measurement results received from the UE. If more than one thresholds are present, the received radio measurements must exceed all thresholds in order to satisfy the indicated radio conditions. The target eNB shall, if supported, report the measurement results to the source NR node by including the Inter-System Handover Report IE (defined in TS 38.

413 [44]) in the eNB CONFIGURATION TRANSFER message only if:

- there is either a single source NR related cell whose measurement results exceed the threshold(s) for the whole measurement duration, or a group of source NR associated cells which together provide such coverage; and - the above is fulfilled for the whole measurement duration, in which case the Early IRAT HO IE contained in the

Inter-System Handover Report IE (defined in TS 38. 413 [44]) shall be set to "false", or the above is fulfilled

until the UE is handed over back to NR within the measurement duration, in which case the Early IRAT HO IE contained in the Inter-System Handover Report IE (defined in TS 38. 413 [44]) shall be set to "true".

The cells that exceed the threshold in the first UE measurement report are included in the Inter-system Handover Report.

If the UE Radio Capability ID IE is included in the HANDOVER REQUEST message, the eNB shall, if supported, use it as defined in TS 23.401 [11].

If the DAPS Request Information IE is included for an E-RAB in the Source eNB to Target eNB Transparent Container IE within the HANDOVER REQUEST message, the target eNB shall consider that the request concerns a DAPS Handover for that E-RAB, as described in TS 36.300 [14]. The target eNB shall include the DAPS Response information List IE in the Target eNB to Source eNB Transparent Container IE within the HANDOVER REQUEST ACKNOWLEDGE message, containing the DAPS Response Information IE for each E-RAB requested to be configured with DAPS Handover.

8.4.2.3 Unsuccessful Operation

HANDOVER REQUEST

MME

HANDOVER FAILURE target

eNB

Figure 8.4.2.3-1: Handover resource allocation: unsuccessful operation

If the target eNB does not admit at least one non-GBR E-RAB, or a failure occurs during the Handover Preparation, it shall send the HANDOVER FAILURE message to the MME with an appropriate cause value.

If the target eNB does not receive the CSG Membership Status IE but does receive the CSG Id IE in the HANDOVER REQUEST message and the CSG Id does not correspond to the CSG Id of the target cell, the target eNB shall send the

If the target eNB does not receive the CSG Membership Status IE but does receive the CSG Id IE in the HANDOVER REQUEST message and the CSG Id does not correspond to the CSG Id of the target cell, the target eNB shall send the